Commit 304b3f2b authored by Tejun Heo's avatar Tejun Heo
Browse files

sched: Allow sched_cgroup_fork() to fail and introduce sched_cancel_fork() 



A new BPF extensible sched_class will need more control over the forking
process. It wants to be able to fail from sched_cgroup_fork() after the new
task's sched_task_group is initialized so that the loaded BPF program can
prepare the task with its cgroup association is established and reject fork
if e.g. allocation fails.

Allow sched_cgroup_fork() to fail by making it return int instead of void
and adding sched_cancel_fork() to undo sched_fork() in the error path.

sched_cgroup_fork() doesn't fail yet and this patch shouldn't cause any
behavior changes.

v2: Patch description updated to detail the expected use.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarDavid Vernet <dvernet@meta.com>
Acked-by: default avatarJosh Don <joshdon@google.com>
Acked-by: default avatarHao Luo <haoluo@google.com>
Acked-by: default avatarBarret Rhoden <brho@google.com>
parent df268382

include/linux/sched/task.h

+2 −1
Original line number Diff line number Diff line
@@ -63,7 +63,8 @@ extern asmlinkage void schedule_tail(struct task_struct *prev); 
extern void init_idle(struct task_struct *idle, int cpu);



extern int sched_fork(unsigned long clone_flags, struct task_struct *p);

extern void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs);

extern int sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs);

extern void sched_cancel_fork(struct task_struct *p);

extern void sched_post_fork(struct task_struct *p);

extern void sched_dead(struct task_struct *p);

kernel/fork.c

+10 −5
Original line number Diff line number Diff line
@@ -2363,7 +2363,7 @@ __latent_entropy struct task_struct *copy_process( 


	retval = perf_event_init_task(p, clone_flags);

	if (retval)

		goto bad_fork_cleanup_policy;

		goto bad_fork_sched_cancel_fork;

	retval = audit_alloc(p);

	if (retval)

		goto bad_fork_cleanup_perf;
@@ -2496,7 +2496,9 @@ __latent_entropy struct task_struct *copy_process( 
	 * cgroup specific, it unconditionally needs to place the task on a

	 * runqueue.

	 */

	sched_cgroup_fork(p, args);

	retval = sched_cgroup_fork(p, args);

	if (retval)

		goto bad_fork_cancel_cgroup;



	/*

	 * From this point on we must avoid any synchronous user-space
@@ -2542,13 +2544,13 @@ __latent_entropy struct task_struct *copy_process( 
	/* Don't start children in a dying pid namespace */

	if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {

		retval = -ENOMEM;

		goto bad_fork_cancel_cgroup;

		goto bad_fork_core_free;

	}



	/* Let kill terminate clone/fork in the middle */

	if (fatal_signal_pending(current)) {

		retval = -EINTR;

		goto bad_fork_cancel_cgroup;

		goto bad_fork_core_free;

	}



	/* No more failure paths after this point. */
@@ -2622,10 +2624,11 @@ __latent_entropy struct task_struct *copy_process( 


	return p;



bad_fork_cancel_cgroup:

bad_fork_core_free:

	sched_core_free(p);

	spin_unlock(&current->sighand->siglock);

	write_unlock_irq(&tasklist_lock);

bad_fork_cancel_cgroup:

	cgroup_cancel_fork(p, args);

bad_fork_put_pidfd:

	if (clone_flags & CLONE_PIDFD) {
@@ -2664,6 +2667,8 @@ __latent_entropy struct task_struct *copy_process( 
	audit_free(p);

bad_fork_cleanup_perf:

	perf_event_free_task(p);

bad_fork_sched_cancel_fork:

	sched_cancel_fork(p);

bad_fork_cleanup_policy:

	lockdep_free_task(p);

#ifdef CONFIG_NUMA

kernel/sched/core.c

+7 −1
Original line number Diff line number Diff line
@@ -4609,7 +4609,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) 
	return 0;

}



void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)

int sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)

{

	unsigned long flags;
@@ -4636,6 +4636,12 @@ void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs) 
	if (p->sched_class->task_fork)

		p->sched_class->task_fork(p);

	raw_spin_unlock_irqrestore(&p->pi_lock, flags);



	return 0;

}



void sched_cancel_fork(struct task_struct *p)

{

}



void sched_post_fork(struct task_struct *p)